Hannibal did some digging on the architecture at the heart of the Xbox 360 and …

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Introduction

When word first got out that Microsoft was planning to get into the game console business, I was skeptical. First, I was skeptical that the rumors were true, and when they turned to be true I was skeptical that the console would have any impact on the market. Today, as an Xbox owner myself, I'm glad to say I was wrong. Microsoft was able to leverage their software expertise and deep pockets to rapidly develop a console that didn't just have an impact on the console market, but went from zero to second place in terms of market share.

Despite the fact that Microsoft scored a touchdown with the Xbox, there's no denying that the console was something of a "Hail Mary" pass. With a slim, 19-month gap between the Xbox program's start to the shipment of the first unit, the Xbox didn't exactly represent a major investment of resources for the world's number one software maker. However, things were different this time around.

Microsoft started work on the successor to the Xbox in 2002, and they went into the project gunning for the top spot in the console market. Unlike the original Xbox's Intel x86 CPU and nVidia-based graphics core, the hardware that powers the Xbox 360 is custom-made from the ground up to run games, high-definition video, and digital audio.

In a move that surprised all of us, Microsoft tapped IBM to design the microprocessor that powers the Xbox 360. IBM drew on the results of the same Broadband Processor Architecture (BPA) initiative that produced the Playstation 3's Cell processor in order to furnish the next-generation Xbox with a truly next-generation core that looks set to last at least the five-year life of the average game console.

Codenamed Xenon, the multicore PowerPC CPU that IBM designed for the Xbox 360 boasts a number of unique features that set it apart from any microprocessor seen to date. The present article covers these features in detail, from the processor's triple-core design, to its caches, deep pipeline, lack of an instruction window, and expected performance.

Before we talk in detail about the way that IBM put together the Xenon CPU, we should first discuss Microsoft's vision for the role that Xenon should play in powering the next generation of games. Thus Part I of this series will be devoted to exploring the types of applications for which the Xbox 360 was designed, with a particular emphasis on 3D gaming and the real-time procedural synthesis of in-game geometry.